With advance in the miniaturization of personal computers, video cameras and portable telephones or the like, in a field of information-related devices and communication devices, as a power source for the devices, because of high energy density, lithium secondary batteries are put into practical use and widely commercialized. On the other hand, in the field of automobiles as well, because of the environmental problems and resource problems, electric cars are urged to develop. Also as a power source of the electric cars, lithium secondary batteries are under study.
In the lithium secondary battery, as one that can obtain a 4V class operational voltage, positive electrode active materials such as LiCoO2 and LiNiO2 having a layered rock salt structure, LiMn2O4 having the spinel structure and lithium transition metal composite oxides obtained by partially substituting the above compounds with other elements are well known. Furthermore, in recent years, compounds having an olivine structure such as compounds represented by a general formula LiMPO4 (M=Mn, Fe, Co, Cu, V), because of being theoretically large in the capacitance, are expected as promising materials.
For instance, in Japanese Patent Application National Publication (Laid-Open) No. 2004-529059, a method for manufacturing LiMPO4 powder, which intends to obtain LiMPO4 having controlled dimension and shape, is disclosed. Furthermore, in Japanese Patent Application Laid-Open (JP-A) No. 2004-303496, a method for manufacturing LinMPO4 by use of inexpensive materials such as metal chlorides or the like is disclosed. Still furthermore, in WO 00/60679, a method for manufacturing a positive electrode active material characterized in mixing solid powdery raw materials, followed by sintering, and adding a reducing agent at the sintering is disclosed. Furthermore, in JP-A No. 11-25983, lithium battery active materials having an olivine structure and represented by a general formula LiM1-xMexPO4 are disclosed.
However, in all of the Japanese Patent Application National Publication (Laid-Open) No. 2004-52909, JP-A No. 2004-303496, WO 00/600679, and JP-A No. 11-25983, in order to obtain LiMPO4 and so on, a sintering method that necessitates to heat up to substantially 800° C. is used. From a viewpoint of such as saving energy, a method that enables to obtain LiMnPO4 which has an excellent crystalline and a high purity at temperatures lower than that in a conventional method is in demand.